This invention relates to an electrochemical cell and in particular to a circular structural frame with spherical anolyte and catholyte surfaces for use in an electrochemical cell.
It is well established that various chemicals can be produced in an electrochemical cell containing an anode and a cathode. For example, alkali metal chlorates, such as sodium chlorate, have been formed electrolytically from a sodium chloride brine in cells without a separator positioned between the anode and the cathode.
When a separator, such as a liquid permeable asbestos or polytetrafluoroethylene diaphragm or a substantially liquid impervious ion exchange membrane, is used in a cell to electrolyze a sodium chloride brine, the electrolytic products will normally be gaseous chlorine, hydrogen gas, and an aqueous solution containing sodium hydroxide.
For a number of years, gaseous chlorine has been produced in electrolytic cells wherein an asbestos diaphragm was interposed between finger like anodes and cathodes interleaved together. During the past several years it has become apparent that the use of substantially liquid impermeable cation exchange membrane may be preferable to the well established diaphragm in instances where a higher purity, for example a lower sodium chloride content, higher sodium hydroxide product is desired. It was found to be more convenient to fabricate ion exchange type electrochemical cells from relatively flat or planar sheets of ion exchange membrane rather than to interleave the membrane between the anode and cathode within the older finger like cells used with asbestos diaphragms.
The newer, so called flat plate bipolar electrochemical cells using a planar sheet of ion exchange membrane to separate the anolyte from catholyte compartments also have a plurality of solid, liquid impervious frames adapted to support the anode on one side and the cathode on the opposite side. These frames have previously been constructed of materials such as metal and plastic. Most commercial cells to date are fabricated from metal due to its superior strength qualities. In any electrochemical cell, including both monopolar and bipolar cells, there is a possibility that electrolyte may leak from within the cell to the exterior. In instances where such leakage has occurred in cells with iron or other ferrous type frames, it was found that the iron frame corroded or was itself electrolytically attacked. Flat plate plastic frames are not generally subject to the electrolytic attack, but have limitations on internal and differential pressure due to the geometry of the cell, namely the fact that it is quite thin in one dimension and quite large in the other two dimensions. This type of chamber is exposed to significant loading on the peripheral flange and center board with even modest increases in internal and/or differential pressure.
Nonrectangular cells have been attempted heretofore. As an example U.S. Pat. No. 755,247 shows nested plans in the manufacture of sulfuric acid. U.S. Pat. No. 4,309,264 shows circular planar cell members captured between facing and opposing end plates. It is submitted that maintaining a planar cell of any geometric profile, whether rectangular or circular, still exposes the center board to the same problems in handling the load which occurs internally within the cell as a result of increases in differential pressure. That is, should the cell be operated at any differential pressure level above atmospheric pressure, the large surface area of the cell exposed to the loading due to the differential pressure risks center board deflection which can damage the cation exchange membrane and can also cause shorting between adjacent cells.
It is desired to provide a structural frame for use in pressure operated electrochemical cells which would eliminate or minimize the deflection of the center board that is associated with those cell designs used by the prior art.